1. Field of the Invention
This invention relates to a method for making soluble zirconium and hafnium organic acid complexes.
2. Description of the Previously Published Art
Complexes of zirconium and hafnium with organic acids have several practical applications in industry. The most prominent one are related to the ability of these metal ions to serve as cross-linking agents for certain kinds of organic polymers which are used, for example, in the manufacture of paper. These applications require the complex containing the metal ion to be soluble in such media as alcohols. For several reasons it is desired that the complexes be obtainable as dry, free-flowing powders. This desire arises from economic and convenience criteria. It is usually undesirable to ship large volumes of a low-cost liquid over long distances. Furthermore, in using such chemicals, dry free-flowing powders are highly desirable for ease of transport and mixing.
Propionic acid complexes of zirconium are known and commercially available such as Magnesium Elektron's Z-plex (TM) 9700. However, reactions intended to prepare complexes from commercial starting materials often produce unsatisfactory products, i.e, ones which do not pass the solubility tests. A typical solubility test includes dissolving at least 65 g in 100 ml of isopropanol and at least 150 g in 100 ml of ethanol. Authoritative literature, however, fails to explain either the means or the reaction mechanisms for achieving products which pass such tests.
For example Blumenthal in "The Chemical Behavior of Zirconium" Van Nostrand, Princeton 1958, discuses formation of zirconium acetate complexes in detail, but on page 317 comments that compounds of other short-chained alkyl carboxylic acids have been studied only superficially. Blumenthal states that while carbonated hydrous zirconia is dissolved by formic acid and acetic acid, it is not dissolved by propionic acid. This statement by Blumenthal shows that this area is poorly understood since it has been discovered that zirconium basic carbonate does dissolve in an excess propionic acid.
In the book "Metal Carboxylates" Academic Press, London 1983, Mehrotra and Bohra discuss the behavior of zirconium acetates, but not synthesis of propionates. Page 240 incorrectly refers to a MO(O.sub.2 CC.sub.2 H.sub.5).sub.2.H.sub.2 O compound, but this is really about butyrates made by a different and commercially insignificant route.
3. Objects of the Invention
It is an object of this invention to provide a process for making organic acid complexes of zirconium and hafnium which are obtainable as dry powders and which are rapidly and readily soluble in alcohols.
It is a further object of this invention to provide a process for making propionic acid complexes of zirconium and hafnium which are obtainable as dry powders and which are rapidly and readily soluble in alcohols.
It is a further object of this invention to derive such complexes from inexpensive and commercially available precursors.
It is a further object of this invention to produce a process wherein high efficiencies of conversion to product of the zirconium and hafnium and also of the propionic acid are achieved.
It is a further object of this invention to provide a process which has a minimal impact on the environment by discharging a minimum amount of pollutants to the air and water.
These and further objects of the invention will become apparent from the following description of the invention.